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Block loadout surveys

Read time: 6 minutes

Since the 1940s shipbuilding practice has undergone massive changes, adopting new technologies. These days, most ships are constructed from prefabricated units. These are assembled into blocks, which need to be transported to the shipyard to be assembled. Loading and discharging as well as lashing and securing of such heavy lift project cargo demands specialist supervision.

Historically, ships were built on slipways, working from the bottom upwards. The huge war-time demand for ships led to the application of mass production techniques in shipbuilding. And as ship sizes increased, the amount of steel used in shipbuilding demanded a new approach: building ship sections as units.

Today, all vessels are prefabricated to various degrees. Units are assembled into larger structures. These larger structures are called blocks. According to Eyres & Bruce (2012) a block is an assembly of two or more units into a bottom or side block, weighing up to 200 tonnes. So-called “grand blocks” or “mega blocks” can be the full width of the ship, weighing up to 500 tonnes.

Outfitted units, combined into blocks, may include machinery, pipework and other systems. To save costs, these units are not built at the shipbuilding yard, but at other locations. And in view of the size and weight, the blocks need to be transported by sea. Loadout is the process of moving heavy structures from land onto a vessel.

Loadout survey: the scope

In our capacity as Marine Warranty Surveyors, Van Ameyde Krogius were instructed to supervise and check the loading and securing operations of hull blocks for two newbuilding projects. These projects concerned two expedition cruise vessels, designed for 150 passengers each.

The scope of our work included:

  • review of the plans and drawings, ranging from block specifications and certificates for lashing equipment to the methods of loading and stowage, passage planning and shipper’s instructions
  • site survey and overseeing the loadout operations
  • lashing and securing survey
  • issuing the Certificate of Approval prior to the voyage, subject to proper adoption of our recommendations, of course
  • reporting

Let’s take a closer look at one of the loadout surveys that we conducted as part of this project.

Preparing the survey

In preparation, we carefully reviewed the Transport Manual issued by the carriers. This included all the plans and drawings mentioned under the scope. We also paid close attention to the ship stability calculations. The stowage plan had factored in the fact that some of the blocks would extend over the vessels’ sides. Three blocks would be loaded via the stern and two via the starboard side.

Loading

The vessel was moored stern to and a KAMAG self-propelled multi-axle transporter was used for loading. The blocks of the first shipment were fitted with lifting lugs, to allow them to be lifted off the vessel at Helsinki. Later shipments used the ro-ro method for both loading and discharging.

You can imagine the importance of continuously adapting the vessel’s ballast, from when the vessel first picks up load up to when the entire structure is in position on board. When in position, the transportation framework of the block is lowered onto the supporting blocks. Close inspection of the supporting blocks showed that part of the grillage transportation framework was deformed. To ensure proper support, plywood sheets were packed into the gaps.

Once the narrower blocks were in position, the blocks extending over the sides were loaded sideways. For this purpose, the vessel was turned, berthing alongside. As you can see in the photograph, this was an extremely tight fit.

Lashing and securing

To secure the blocks, lashing lugs had to be welded to the transportation framework. Another area of inspection is the transverse lashing arrangements. Wire rope slings were connected to the welded lashing lugs. Clamp hooks were fitted with welded stoppers and D rings were welded to the deck plating.

There are advanced calculation methods for the lashing requirements. However, the rule-of-thumb method is more robust. The maximum securing load (MSL in kN) is the load capacity for any device used to secure cargo. The rule-of-thumb determines that the total of the MSL values of the securing devices on each side of the block should equal the weight of the block. Suffice to say, that the same unit is used when comparing MSL and weight: 1 kN = 100 kg = 0.1 tonne.

For instance, the MSL of welded sea fastenings is 10 kN (1 tonne) per cm of weld run. The weld must of course be of good quality, with sufficient penetration. The thickness should be about 1 cm. A D ring weld run of 10 cm supports an MSL of 10 tonnes (100 kN).

We established that the lashing arrangements met the requirements. The welding work too was inspected by us, showing some unfinished work, which was subsequently completed in accordance with our recommendations. In addition, weldments were randomly tested for cracks using the magnetic particle test method. No cracks were found.

Beside the gaps in the supporting framework and the unfinished welding work, we found that some loose items were stowed in the block assemblies. To remedy this, sea fastenings were applied.

Certificate of Approval

Once the recommended work was finished, we checked the work, with which the attending surveyor was entirely satisfied. Subsequently, the Certificate of Approval was issued.

Mission completed successfully

From September 2020 to May 2021 we supervised the loadout operations, comprising nine shipments of a total of 46 blocks. A massive operation, which was brought to a successful completion thanks to the close cooperation of the shipbuilder, the block manufacturer, the carriers and, of course, the Marine Warranty Surveyors of Van Ameyde Krogius!

 

Source
Eyres, D.J. and Bruce, G.J. (2012.) Ship Construction, 7th edition 2012. Butterworth-Heinemann

 

For other reading, we recommend looking into one of our earlier blogs, ‘Airflow in reefer containers: circulation and ventilation explained’

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